<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>only-of-type</title>
<style type="text/css">
article:only-of-type {
	background: #f00;
}
</style>
</head>
<body>
<section>
	<article>1</article>
	<article>2</article>
</section>
<section>
	<article>3</article>
</section>
<section>
	<div>4</div>
	<article>5</article>
	<div>6</div>
</section>
<section>
	<div>7</div>
	<article>8</article>
	<article>9</article>
	<div>10</div>
</section>
</body>
</html>